Student Exploration: Mystery Powder Analysis

Name: _H_a_n_n__a_h_S__o_n_n_e_n_t_a_g_____________________ Date: _1_2_/_1_5_/1_1_________________

Student Exploration: Mystery Powder Analysis

Vocabulary: Biuret solution, iodine solution, litmus paper, vinegar

Prior Knowledge Questions (Do these BEFORE using the Gizmo.) A white powder is found spilled on the kitchen floor of a crime scene. A similar powder is found on the shoes of a suspect in the crime.

1. What are some powders that you might find on the kitchen floor? _____________________ _s_a_lt_,_f_lo_u_r_, _s_u_g_a_r_, _b_a_k_in__g_s_o_d_a_,__g_a_rl_ic__p_o_w_d_e__r,__________________________________

2. How could you tell if the powder was salt, sugar, flour, or baking soda? ________________ _Y_o_u__ta_k_e__s_a_m__p_le_s__a_n_d__ta_s_t_e__th_e_m__.___________________________________________

Gizmo Warm-up The Mystery Powder Analysis GizmoTM allows you to use a variety of tests to identify unknown substances. To start, drag the Baking soda test tube into the "Place tube here" area.

1. Under Appearance, click Test. Is baking soda a fine powder (no visible grains), or is it coarse (visible grains)?

_it_a__c_o_a_r_s_e_g__ra_i_n_t_h_a_t_i_s_v_i_si_b_le____________________

2. Litmus paper is an indicator of acids and bases. Under Litmus test, click Test. Which of the following results occurred? (Circle the answer.)

A. Both strips red (acid)

C. One red, one blue strip (neutral)

B. Both strips blue (base)

3. Some substances react with vinegar to produce carbon dioxide, visible as bubbles. yes

Under Vinegar test, click Test. Does the vinegar bubble? ________________________

4. The blue Biuret solution turns bright purple in the presence of proteins. Iodine solution turns dark purple in the presence of starch. Try each of these tests.

Does baking soda contain protein? _y_e_s___ Does baking soda contain starch? _n_o____

Activity A:

Known substances

Get the Gizmo ready:

? Click Reset. ? Be sure the Known substances are selected.

Question: What are the properties of baking powder, baking soda, corn starch, gelatin, and salt?

1. Collect data: Use the Gizmo to test the five known substances. Fill in the results below.

Substance

Baking powder Baking

soda Corn starch

Appearance (coarse or fine?)

fine

fine

fine

Litmus

Vinegar

Biuret

(acid or base?) (bubbles?) (protein?)

acid and base bubbles

no

base

bubbles

no

acid and base no bubbles no

Iodine (starch?)

yes

no

yes

Gelatin

coarse

acid

no bubbles yes

no

Salt

coarse

acid and base no bubbles no

no

2. Analyze: Look at the results of your tests. A. Which substance(s) are acids? _g_e_la__ti_n_, _s_a_lt_, _c_o_r_n_s_t_a_rc_h__, _b_a_k_in_g__p_o_w__d_e_r,_______ baking powder, baking soda, corn starch, salt B. Which substance(s) are bases? _________________________________________ baking powder, baking soda, C. Which substance(s) react with vinegar? ___________________________________ gelatin D. Which substance(s) contain protein? ______________________________________ E. Which substance(s) contain starch? _b_a_k_in__g_p_o_w__d_e_r_, _c_o_rn__s_t_a_rc_h_,______________

3. Apply: Suppose you find a mystery powder. It is coarse in appearance, has a neutral pH, and does not react with vinegar, Biuret solution, or iodine. salt Of the five substances listed here, which is it most likely to be? _______________________

4. Challenge: Baking powder is a combination of three substances, two of which are other "known" substances in the Gizmo. What are the two "known" substances in baking powder? _b_a_k_in__g_p_o_w__d_e_r_a_n_d__c_o_r_n_s_t_a_r_c_h______________________________________________

Activity B:

Unknown substances

Get the Gizmo ready:

? Click Reset. ? Under Select a sample, choose Unknown. ? Check that the Standard mystery set is displayed.

(If not, click Refresh or Reload on your browser.)

Question: How can you identify unknown substances?

1. Identify: Test tubes 1-5 are all contain single substances. Run the five tests on these powders, and identify the substance in each tube.

Sample 1 2 3 4 5

Appearance Litmus Vinegar Biuret Iodine

fine

acid and base no bubbles blue/no protein dark purple/starch

fine

base

bubbles blue/ no protein red/no starch

course

acid and base no bubbles blue/no protein red/no starch

fine

acid and base bubbles blue/no protein dark purple/starch

coarse

acid

no bubbles light purple/protein red/no starch

Substance corn starch

baking soda salt

baking powder gelatin

2. Identify: Test tubes 6-10 all contain mixtures of two substances. Run the five tests on these powders, and identify the TWO substances in each tube. Sample Appearance Litmus Vinegar Biuret Iodine Substances 6

7

8

9

10

3. Analyze: Are there any situations where there is more than one correct answer? Explain. _________________________________________________________________________ _________________________________________________________________________

(Activity B continued on next page)

Activity B (continued from previous page) 4. Challenge: Test tubes 11-15 all contain mixtures of three substances. Run the five tests on

these powders, and identify the THREE substances in each tube. (Note: Sometimes there will be more than one possible answer.)

Sample Appearance Litmus Vinegar Biuret Iodine Substances

11

12

13

14

15

5. Analyze: Based on your experiences, answer the following. A. Why is it hard to tell if a mixture contains salt? ______________________________ ___________________________________________________________________ ___________________________________________________________________ B. How can you tell if a sample contains baking soda and cornstarch or baking powder? ___________________________________________________________________ ___________________________________________________________________

6. On your own: For further practice, click New sample. As in the Standard mystery set, the test tubes in the first row each contain one substance, the test tubes in the second row contain two, and the test tubes in the third row contain three. You may find new substances you haven't seen before. Good luck! (Note: At this point, the contents of the tubes are randomized, so results will vary.)

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